冷酷な公爵様は名無しのお飾り妻がお気に入り～悪女な姉の身代わりで結婚したはずが、気がつくと溺愛されていました～

The ruthless duke has a crush on his nameless figurehead wife - he married her to take the place of his wicked sister, but before he knew it, he was doting on her